3.5. Stability

3.5. Stability

When a zone is modified by an UPDATE operation, the server must
commit the change to nonvolatile storage before sending a response to
the requestor or answering any queries or transfers for the modified
zone. It is reasonable for a server to store only the update records
as long as a system reboot or power failure will cause these update
records to be incorporated into the zone the next time the server is
started. It is also reasonable for the server to copy the entire
modified zone to nonvolatile storage after each update operation,
though this would have suboptimal performance for large zones.